JP7252241B2 - Wearable cuff control - Google Patents

Description

The present application relates to devices and methods for controlling wearable cuffs used to measure blood pressure.

Blood pressure (BP), more precisely arterial blood pressure, is the pressure that circulating blood exerts on the walls of arteries. It is one of the key vital signs for establishing patient health and therefore needs to be monitored for at-risk patients. Blood pressure is a periodic signal that rises with each contraction of the heart and falls between heart beats. It is commonly expressed in systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial blood pressure (MAP), where systolic blood pressure is the highest blood pressure during the cardiac cycle and diastolic blood pressure is the blood pressure during the cardiac cycle. Diastolic blood pressure, mean arterial blood pressure, is the average blood pressure during the cardiac cycle.

Various techniques exist for measuring blood pressure, which are classified as invasive or non-invasive measurement techniques. Generally, non-invasive measurement techniques are cuff-based, which require placing an inflatable cuff around the subject's extremity (usually the upper arm). The pressure within the cuff is then varied to infer blood pressure. There are two common methods of using the cuff in this way, called the auscultatory method and the oscillometric method, respectively.

Auscultation for blood pressure measurement is based on the appearance and disappearance of sounds made by the artery under the cuff during periods of varying cuff pressure. These sounds are called Korotkoff sounds. The pressure at which the Korotkoff sound appears and disappears indicates DBP and SBP, where the Korotkoff sound appears at each heart beat between DBP and SBP. Sound measurements can be made manually with a stethoscope placed over the artery just below the cuff, or can be made automatically with a microphone below the cuff.

In oscillometric methods for blood pressure measurement, systolic and diastolic blood pressure values are based on small volume or pressure oscillations induced in the cuff with each beat. The amplitude of these volume or pressure oscillations depends on the difference between the cuff pressure and the actual arterial blood pressure. Systolic and diastolic pressures are determined as cuff pressures where volume or pressure oscillations have an amplitude that is a percentage of the maximum oscillation amplitude. These fractions are typically heuristically determined.

For both auscultatory and oscillometric methods, mean arterial pressure is generally calculated as MAP=2/3*DBP+1/3*SBP.

Oscillometric and auscultatory methods can be performed during cuff inflation or during cuff deflation. Conventionally, measurements during contraction are used. There, the cuff is rapidly inflated to a level above the SBP where blood flow in the artery beneath the cuff is blocked, and then the cuff pressure is reduced gradually or in steps. During contraction, volume or pressure oscillations or Korotkoff sounds are measured. Contraction stage measurement is well established but presents the problem of causing discomfort to the subject. In particular, subjects are exposed to relatively high cuff pressures for a period of time, and pressures above a certain level may result in accumulation of venous blood (i.e., venous pooling), either due to the pressure exerted by the cuff itself, or in the clamped extremity. Because of this, it can be uncomfortable and even painful. The longer these pressures are applied to the subject, the higher the subject's discomfort level.

Another problem with using deflation-based blood pressure measurements is that the process of inflating and then deflating the cuff is rather lengthy, with each measurement during deflation typically taking 40 seconds to complete. A predetermined maximum pressure level must also be reached before the deflation procedure begins, thus exposing the subject to a maximum cuff pressure higher than that required for blood pressure measurements. Furthermore, the inherent variability of blood pressure over time can skew a single blood pressure measurement.

Because of these problems, devices have been developed to determine the vibrations during inflation of blood pressure cuffs. These devices can reduce discomfort. This is because blood pressure measurements can be made in a shorter time using the inflation phase rather than the deflation phase. In order to keep the measurement time as short as possible without sacrificing accuracy, the optimal number of oscillations to determine the blood pressure (i.e. enough to ensure a certain accuracy, but no more) The inflation rate of the cuff can be made pulse rate dependent so that there is a Thus, once the pressure range of interest is achieved in the inflation phase, pressure relief can be initiated to reduce overall measurement time and pressure-based discomfort. An example of a device for adapting the inflation rate of wearable cuffs is described in US9,017,264.

Nevertheless, there are also challenges associated with existing devices that adapt the inflation rate to the subject's pulse rate. To accomplish this, the subject's pulse rate must be determined, which requires an external sensor or analysis of pressure oscillations within the cuff. In the latter case, a constant initial inflation rate can be used, during which the subject's pulse rate is determined. This initial inflation rate is modified when the pulse rate is known. Blood pressure can be estimated from all of the pressure oscillations in the signal (including pressure oscillations during pulse rate determination).

However, changes in inflation rate induce artifacts (or transient effects) in the signal, which result in portions of the signal surrounding changes in inflation rate being unusable for blood pressure determination. This negatively impacts the accuracy of blood pressure measurements, especially when velocity changes (and thus artifacts) occur around maximum oscillation amplitudes or at oscillation amplitudes related to systolic or diastolic blood pressure. there is a possibility. In the worst case, the induced artefacts may prevent normal measurements from being made (e.g., the measurement may be stopped prematurely due to induced oscillations), or the induced artefacts may lead to erroneous measurements. may be present and may give rise to an erroneous diagnosis.

As noted above, a limitation of existing techniques for controlling wearable cuffs for blood pressure measurements is that artifacts induced by varying the inflation rate of the wearable cuff can be observed in blood pressure measurements taken during inflation of the wearable cuff. This is because it can have a negative impact on accuracy. Thus, it would be beneficial to address these limitations.

Thus, according to a first aspect there is provided an apparatus for controlling a wearable cuff used for measuring blood pressure. The wearable cuff is inflatable to pressurize the target measurement site. The device is configured to initiate inflation of the wearable cuff at a first inflation rate and to vary the first inflation rate during inflation of the wearable cuff. The first inflation rate is changed at a rate limited to a maximum value.

In some embodiments, the device may be configured to change the first inflation rate to the second inflation rate during inflation of the wearable cuff. In some embodiments, the device may be configured to change the first inflation rate by increasing the first inflation rate during inflation of the wearable cuff. In some embodiments, the device may be configured to alter the first inflation rate by decreasing the first inflation rate during inflation of the wearable cuff.

In some embodiments, the first inflation rate may be changed at a rate that is a maximum value or a rate that is less than the maximum value. In some embodiments, the first inflation rate may be changed at a rate that is variable or may be changed at a rate that is constant. In some embodiments, the maximum can be 16 mmHg/s ² or less.

In some embodiments, the device may be configured to change the first inflation rate based on the pulse rate obtained from the subject during inflation of the wearable cuff at the first inflation rate.

In some embodiments, the maximum value may be a fixed value. In some embodiments, the maximum value may be a value dependent on at least one parameter. In some embodiments, the at least one parameter is a pulse rate obtained from the subject during inflation of the wearable cuff at the first inflation rate, pulse rate within the wearable cuff during inflation of the wearable cuff at the first inflation rate, and any one or more of the amplitude of the signal indicative of the pressure oscillations detected in, the difference between the first inflation rate and the second inflation rate, and one or more characteristics of the system comprising the wearable cuff may contain. In some embodiments, the one or more characteristics of the system can include any one or more of the size of the wearable cuff and the resistance detected by the system.

In some embodiments, the device is further configured to acquire a signal indicative of pressure oscillations detected within the wearable cuff during inflation of the wearable cuff and determine the blood pressure value of the subject based on the acquired signal. may In some embodiments, the acquired signal may be in the frequency range of 0.5 Hz to 5 Hz.

According to a second aspect, a system is provided for use in measuring blood pressure. The system comprises a device as described above and a wearable cuff that is inflatable to pressurize the target measurement site.

According to a third aspect, a method is provided for controlling a wearable cuff used to measure blood pressure. The wearable cuff is inflatable to pressurize the target measurement site. The method includes initiating inflation of the wearable cuff at a first inflation rate and varying the first inflation rate during inflation of the wearable cuff. The first inflation rate is changed at a rate limited to a maximum value.

According to a fourth aspect, there is provided a computer program product comprising a computer readable medium having computer readable code embodied therein, said computer readable code being adapted for use in a suitable computer or processor. configured to perform the method when executed by the computer or processor.

According to the aspects and embodiments described above, the limitations of existing technology are addressed. In particular, the aspects and embodiments described above limit the rate at which the inflation rate is changed to slowly change the inflation rate. This ensures that artifacts (or transient effects) otherwise induced by changes in the rate of inflation of the wearable cuff are minimized in the signal indicative of pressure oscillations that can be detected within the wearable cuff during inflation, or Provide control of the wearable cuff used to measure blood pressure in such a way that it is removed from those signals.

Thus, the aspects and embodiments described above provide adequate control of the wearable cuff by limiting the rate at which the inflation rate is changed, so that during inflation of the wearable cuff, the wearable cuff can be used more effectively. Accurate blood pressure measurements can be obtained.

Accordingly, the aforementioned limitations associated with existing technologies are addressed using the aspects and embodiments described above.

These and other aspects will be made clear and explained with reference to the embodiments described below.

FIG. 11 is a simplified schematic diagram of a device for use with a wearable cuff according to an exemplary embodiment; FIG. 4 is a block diagram of an apparatus for controlling a wearable cuff in accordance with an exemplary embodiment; FIG. 4 is a flow chart illustrating a method of controlling a wearable cuff according to one embodiment; FIG. 1 is a schematic illustration of an exemplary signal exhibiting artifacts according to existing techniques; FIG. FIG. 4 is a pictorial illustration of an exemplary signal showing reduced artifacts according to one embodiment; FIG. 5 is a pictorial illustration of an exemplary signal showing reduced artifacts according to another embodiment; FIG. 5 is a pictorial illustration of an exemplary signal showing reduced artifacts according to another embodiment; FIG. 5 is a pictorial illustration of an exemplary signal showing reduced artifacts according to another embodiment; FIG. 5 is a pictorial illustration of an exemplary signal showing reduced artifacts according to another embodiment;

Exemplary embodiments are described with reference to the following drawings, which are exemplary only.

Provided herein is a device for controlling a wearable cuff (or clamp unit) for use in blood pressure measurement that overcomes the limitations of existing technology. The wearable cuffs referred to herein are inflatable to pressurize the subject's (eg, patient's) measurement site. Thus, the wearable cuff can pressurize the artery at the measurement site of interest. Typically, the wearable cuff can be supplied with a fluid (eg, gas such as air, or any other fluid) suitable for inflating the wearable cuff. The wearable cuff may be inflatable such that the pressure of the fluid within the wearable cuff pressurizes the target measurement site (and thus the artery of the target measurement site).

The wearable cuff is configured to be worn (eg, wrapped, attached, or secured) to or about a subject's measurement site. The subject's measurement site can be any site of the subject's body that is suitable for measuring the subject's blood pressure, and can be any site of the subject's body, including, for example, an artery. For example, the subject's measurement site can be the subject's extremity, eg, the subject's arm (eg, upper arm or forearm). Thus, the wearable cuff can be configured to be worn (eg, wrapped, attached, or secured) over or around a subject's limb.

Briefly, the devices described herein initiate inflation of the wearable cuff at a first inflation rate and vary (or adapt) the first inflation rate during (or during inflation phases) the wearable cuff inflation. ). As described herein, the first inflation rate is changed at a rate limited to a maximum value. The maximum value referred to herein is referred to as the maximum rate at which the first expansion rate is changed, the maximum rate of change in the first expansion rate, or the rate limit (hereinafter "RL"). There is also Thus, the devices described herein are configured to limit the rate at which the first inflation rate is changed. More specifically, the device can be configured to gradually limit the rate at which the first inflation rate is changed to a maximum value. It should be appreciated that gradual changes can be immediate, instantaneous, or non-abrupt. The apparatus can be implemented in multiple ways, using software and/or hardware, to perform various functions described herein. In certain implementations, an apparatus comprises multiple software and/or hardware modules each configured to perform, or configured to perform, individual steps or steps of methods described herein. can have

The apparatus may have one or more processors (e.g., one or more processors) that can be configured or programmed (e.g., using software or computer program code) to perform various functions described herein. microprocessor, one or more multi-core processors and/or one or more digital signal processors (DSP)), one or more processing units, and/or one or more controllers (one or more micro controller, etc.). The apparatus includes dedicated hardware (e.g., amplifiers, preamplifiers, analog-to-digital converters (ADC) and/or digital-to-analog converters (DAC)) to perform some functions and other functions. may be implemented in combination with a processor (eg, one or more programmed microprocessors, a DSP and associated circuitry) for performing.

FIG. 1 shows device 12 using wearable cuff 14 used to measure blood pressure, according to an exemplary embodiment. Thus, system 10 having device 12 and wearable cuff 14 is provided. As previously mentioned, wearable cuff 14 is inflatable to pressurize the measurement site of subject 18 . In the exemplary embodiment shown in FIG. 1, the measurement site of subject 18 is located on the upper arm of subject 18 . Thus, the wearable cuff 14 is worn (eg, wrapped, attached, or secured) to or about the upper arm of the subject 18 in this illustrated exemplary embodiment.

As shown in FIG. 1, in some embodiments, cuff 14 may be coupled or connected to device 12 via at least one supply line (or at least one supply tube) 16, which Also sometimes referred to as at least one pressure supply line (or at least one pressure supply tube) 16 . At least one supply line 16 may be arranged to pressurize the wearable cuff 14 and, consequently, the measurement site of the subject 18 . At least one supply line 16 may be provided for inflating and/or deflating the wearable cuff 14 . As an alternative to at least one supply line 16, in other embodiments (not shown), device 12 may be directly coupled (eg, directly attached) to wearable cuff 14. FIG. As previously mentioned, wearable cuff 14 may be supplied with any fluid suitable for inflating wearable cuff 14 .

Although not shown in FIG. 1, in some embodiments, system 10 can include a pump. The pump may be controllable to inflate the wearable cuff 14 in the manner described herein. In some embodiments, the device 12 described herein may include a pump. Alternatively or additionally, the pump may be external to device 12 (eg, separate from or separate from device 12). The pump can thus be any pump that can be controlled to inflate the wearable cuff 14 . In some embodiments, a pump may be controllable by the controller of device 12 to inflate wearable cuff 14 in the manner described herein. The controller of device 12 may communicate with and/or be connected to the pump in any suitable manner for controlling the pump.

Similarly, although not shown in FIG. 1, in some embodiments system 10 can include a deflation valve. A deflation valve is controllable to deflate the wearable cuff 14 . In some embodiments, the device 12 described herein may include a deflation valve. Alternatively or additionally, the deflation valve may be external to device 12 (eg, separate from or separate from device 12). Accordingly, the deflation valve can be any valve that can be controlled to deflate the wearable cuff 14 . In some embodiments, a deflation valve may be controllable by the controller of device 12 to deflate wearable cuff 14 . The controller of device 12 may communicate with and/or be connected to the deflation valve in any suitable manner for controlling the deflation valve.

Similarly, although not shown in FIG. 1, in some embodiments system 10 may include at least one pressure sensor. At least one pressure sensor may be configured to measure pressure within wearable cuff 14 . In some embodiments, device 12 described herein may include at least one pressure sensor configured to measure pressure within wearable cuff 14 . Alternatively or additionally, at least one pressure sensor external to device 12 (eg, separate or remote from device 12 ) may be configured to measure pressure within wearable cuff 14 . For example, in some embodiments, wearable cuff 14 itself may include at least one pressure sensor configured to measure pressure within wearable cuff 14 . In some embodiments, at least one pressure sensor may be controllable by the controller of device 12 to measure pressure within wearable cuff 14 . A controller of device 12 may communicate with and/or be connected to the at least one pressure sensor in any suitable manner for controlling the at least one pressure sensor.

Similarly, although not shown in FIG. 1, system 10 may include a communication interface (or communication circuitry) in some embodiments. In some embodiments, the device 12 described herein can include a communications interface. Alternatively or additionally, the communication interface may be external to device 12 (eg, separate from or separate from device 12). A communication interface allows device 12 or elements of device 12 to communicate with and/or to one or more other elements, sensors, interfaces, devices or memories (such as any described herein). It may be for enabling connection. For example, the communication interface allows the controller of device 12 to communicate with and/or be connected to any one or more of the pump, deflation valve, and at least one pressure sensor previously described. It may be for A communication interface may allow device 12 or elements of device 12 to communicate and/or connect in any suitable manner. For example, a communication interface allows device 12 or elements of device 12 to communicate and/or connect wirelessly, via a wired connection, or via any other communication (or data transfer) mechanism. may In some wireless embodiments, for example, the communication interface allows device 12 or elements of device 12 to communicate and/or connect using radio frequency (RF), Bluetooth, or any other wireless communication technology. may be enabled.

Similarly, although not shown in FIG. 1, system 10 may include memory in some embodiments. In some embodiments, the devices 12 described herein can include memory. Alternatively or additionally, the memory may reside external to device 12 (eg, separate from or remote from device 12). The controller of device 12 may be configured to communicate with and/or be connected to memory. The memory can comprise any type of non-transitory machine-readable medium, such as random access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), read-only memory (ROM), programmable ROM ( PROM), erasable PROM (EPROM), and electrically erasable PROM (EEPROM) are caches or system memory, including volatile and non-volatile computer memory. In some embodiments, the memory may be configured to store program code that may be executed by a processor to operate device 12 in the manner described herein.

Alternatively or additionally, in some embodiments, the memory may be configured to store information required by or resulting from the methods described herein. For example, in some embodiments, the memory stores the inflation rate described herein, the rate at which the first inflation rate is changed, the maximum value of this rate, any one or more of the blood pressure readings obtained during the course of treatment, any other information required by or resulting from the methods described herein, or any combination of any information. may be configured to store the In some embodiments, the controller of device 12 may be configured to control memory to store information required by or resulting from the methods described herein.

Also, although not shown in FIG. 1, system 10 may include a user interface. In some embodiments, the device 12 described herein can include a user interface. Alternatively or additionally, the user interface may exist external to device 12 (eg, separate from or separate from device 12). The controller of device 12 may be configured to communicate with and/or be connected to a user interface. A user interface may be configured to render (or output, display, or provide) information required by or resulting from the methods described herein. For example, in some embodiments, the user interface displays the inflation rate described herein, the rate at which the first inflation rate is changed, the maximum value of this rate, rendering (or output, display or provide). Alternatively or additionally, the user interface can be configured to receive user input. For example, a user interface may allow a user to manually enter information or instructions, interact with device 12 , and/or control device 12 . Thus, a user interface may be any user interface that enables rendering (or outputting, displaying, or providing) information and, alternatively or additionally, allows a user to provide user input. In some embodiments, the controller of device 12 may be configured to control the user interface to operate in the manner described herein.

For example, a user interface may be one or more switches, one or more buttons, a keypad, keyboard, mouse, touch screen or application (e.g. on a smart device such as a tablet, smartphone, or any other smart device). ), a display or display screen, a graphical user interface (GUI) or other visual element such as a touch screen, one or more speakers, one or more microphones or other audio elements, one or more lights ( light-emitting diode LED lights, etc.), components that provide tactile or tactile feedback (such as a vibration function, or any other tactile feedback component), augmented reality devices (such as augmented reality glasses, or any other augmented reality device), It may include a smart device (such as a smart mirror, tablet, smartphone, smartwatch, or any other smart device) or any other user interface or combination of user interfaces. In some embodiments, the user interface controlled to render the information may be the same user interface that allows the user to provide user input.

Similarly, although not shown in FIG. 1, device 12 may include a battery or other power source for powering device 12 or means for connecting device 12 to a mains power source. It will also be appreciated that device 12 may include any other element or combination of elements than those described herein.

FIG. 2 shows in more detail the device 12 (described above with reference to FIG. 1) for controlling the wearable cuff 14 according to an exemplary embodiment. Referring to FIG. 2, according to this exemplary embodiment, device 12 is pump 22 (eg, the pump described above with reference to FIG. 18 and optionally also to at least one supply tube 16); pressure sensor), and any one or more of an analog filter 26, an oscillation filter 28, a transducer 30, a limiter 31, and a controller or pump controller 32 (eg, those described above with reference to FIG. 1). You can stay.

Referring to FIG. 2, in some embodiments, at least one pressure sensor 24 may be configured to measure pressure within wearable cuff 14 . Transducer 30 may receive pressure measured within wearable cuff 14 from at least one pressure sensor 24 . In some embodiments, transducer 30 is configured to obtain the measured (or actual) inflation rate of wearable cuff 14 by converting the pressure measured within wearable cuff 14 to a pressure rate. may For example, transducer 30 may be configured to take the derivative (more specifically, the time derivative d/dt) of the pressure measured within wearable cuff 14 and convert the measured pressure to a pressure rate. good. The pressure rate can indicate the measured (or actual) inflation rate.

As previously described, inflation of wearable cuff 14 is initiated at a first inflation rate, which is altered during inflation of wearable cuff 14 . In the exemplary embodiment of FIG. 2, limiter 31 is configured to limit the rate at which the first expansion rate is changed to its maximum value. In other words, the limiter 31 is arranged to limit the rate of change of the first inflation speed to a maximum value. More specifically, the limiter 31 can be configured to gradually limit the rate at which the first inflation speed is changed (or the rate of change in the first inflation speed) to a maximum value. As noted above, gradual changes are understood to be changes that are immediate, instantaneous, or not abrupt. A maximum value for the rate at which the first expansion rate is changed can be set by limiter 31 . The limiter 31 is therefore also called an expansion rate change limiter (ISCL) or a rate limiter (RL). In effect, the limiter 31 limits the target rate of change of the first expansion rate (e.g., with a steep change) that the limiter 31 can receive as input to a maximum value (the change in the first expansion rate can be configured to convert the target rate of change of the first expansion rate such that The target rate of change of the first inflation speed limited to the maximum value can be referred to as the limited target rate of change of the first inflation speed.

Controller 32 may be configured to receive a limited target rate of change of the first inflation speed from limiter 31 . The controller 32 is configured to initiate inflation of the wearable cuff 14 at the first inflation rate and to vary the first inflation rate during inflation of the wearable cuff 14 in a conventional manner, but limited to a maximum value. at a rate, ie, based on a limited target rate of change of the first inflation rate that controller 32 receives from limiter 31 . For example, in some embodiments controller 32 may also be configured to receive the measured (or actual) inflation rate of wearable cuff 14 from transducer 30 . According to these embodiments, the controller 32 combines the limited target rate of change of the first inflation velocity received from the limiter 31 and the measured (or actual) inflation rate received from the converter 30 into: It can be configured to convert it into a control signal for output to the pump 22 .

In some embodiments, for example, controller 32 may be configured to compare a limited target rate of change of the first inflation rate to the measured (or actual) inflation rate. Thus, the controller 32 is configured to determine the difference between the measured (or actual) inflation rate and the limited target rate of change of the first inflation rate that the controller 32 receives from the limiter 31. can be done. In these embodiments, controller 32 is configured to control pump 22 based on the difference between the measured (or actual) inflation rate and the limited target rate of change of the first inflation rate. obtain. In some of these embodiments, controller 32 outputs a control signal to pump 22 that minimizes the difference between the first inflation rate limited target rate of change and the measured inflation rate. can be configured as Thus, abrupt changes in the first expansion rate (eg any abrupt steps) and thus corresponding artifacts are minimized or eliminated. At steady state, the difference can be zero. In some embodiments, the change in the first inflation rate can be a change in the first inflation rate from the rate used during pulse rate determination to a pulse rate dependent rate.

A control signal from the controller 32 is thus received by the pump 22 and used to control the pump to inflate the wearable cuff 14 in the manner described herein, indicating the pressure within the wearable cuff 14. Reduce or eliminate otherwise induced artifacts in the pressure signal. The pump 22 may not exactly follow the control signal, but instead may have a constant system response Hpump(s). The system response of the pump, for example, may have some delay and/or overshoot (or ringing) on the step input. In general, the dynamic pump response may be non-linear with pressure and depends on its operating conditions (e.g. drive signal (e.g. drive voltage), rotational speed (e.g. for centrifugal pumps)). In some cases, the actual pump response may therefore be a function of (or dependent on) pressure and be Hpump(s,p).

The air pressure within system 10 (which consists of wearable cuff 14 worn over or around subject 18 and optionally at least one supply tube 16) is based on input received from pump 22 to: It has its own system response. In its simplest form, the pneumatic response can be modeled as a simple resistance/compliance combination Hpneumatic(s). In general, this pneumatic response is non-linear with pressure, so the actual pneumatic response may be a function of pressure (or may be pressure dependent) and will be Hpneumatic(s,p) .

As previously mentioned, the at least one pressure sensor 24 can be configured to measure pressure within the wearable cuff 14 . Also, the at least one pressure sensor 24 may be configured to convert the measured pressure to the electrical domain. For example, at least one pressure sensor 24 may be configured to convert the measured pressure into an electrical signal. The electrical signal may then pass through an analog filter 26, such as an analog electrical low-pass filter (eg, an anti-aliasing filter). Analog filter 26 has a predetermined filter response Hanalogfilter(s). Analog filter 26 may operate as a first order resistor-capacitor (RC) filter. The electrical signal may pass through oscillation filter 28 . An oscillating filter (eg, a digital oscillating filter) 28 can be configured to remove expansion ramps from pressure oscillations. Oscillating filter 28 has a predetermined filter response Hoscfilter(s) to changes in expansion rate. From this filter response, we can know exactly where the filter is implemented as a digital filter.

として書かれることができる。 The total system response from the first expansion rate change to the resulting oscillating signal is a combination of all the responses described above. In the frequency domain, this is

can be written as

Measures can be taken to make the system response independent of pressure. For example, means can include modeling pressure dependent factors and compensating for pressure in a digital manner. Thus, HTotal(s,p) is simplified to HTotal(s), ie the dependence on pressure is removed.

FIG. 3 illustrates a method 300 of controlling wearable cuff 14 used for blood pressure measurement according to an embodiment. As previously mentioned, wearable cuff 14 is inflatable to pressurize measurement site 20 of subject 18 . The method 300 may generally be performed by or under the control of the controller 32 of the device 12 previously described. At block 302, inflation of the wearable cuff 14 is initiated at a first inflation rate. At block 304 , the first inflation rate is changed during inflation of the wearable cuff 14 . For example, in some embodiments, device 12 may be configured to change a first inflation rate to a second inflation rate during inflation of wearable cuff 14 . As previously mentioned, the first inflation rate is changed at a rate limited to the maximum value that can be set by limiter 31 .

In some embodiments, device 12 may be configured to change the first inflation rate by increasing the first inflation rate during inflation of wearable cuff 14 . In other embodiments, device 12 may be configured to vary the first inflation rate by decreasing the first inflation rate during inflation of the wearable cuff. Based on the value of the first inflation rate, device 12 performs the first inflation rate by increasing the first inflation rate during inflation of the wearable cuff or by decreasing the first inflation rate during inflation of the wearable cuff. It may be configured to determine whether to change the inflation rate of 1.

In typical implementations, the change in inflation rate is instantaneous, resulting in a step or "step change" in inflation rate. This rapid inflation rate change has been found to be the cause of induced artifacts in the pressure signal indicative of the pressure within the wearable cuff 14 . Since this artifact propagates into the signal containing the pressure oscillation, it causes an error in the blood pressure measurement obtained by analyzing the pressure oscillation measured by the wearable cuff 14 . The manner in which device 12 controls inflation of wearable cuff 14 by varying the first inflation rate at a rate limited to a maximum value during inflation of wearable cuff 14 includes a pressure signal indicative of the pressure within wearable cuff 14 . and thus from the measured pressure oscillations within the wearable cuff 14 . This allows obtaining more accurate blood pressure measurements.

More specifically, in order to have a valid pressure signal (or pressure envelope), changes in pressure within the wearable cuff 14 due to effects other than pressure oscillations (e.g., artifacts due to changes in the first inflation rate) must be controlled by the wearable. It should be small or negligible compared to the pressure change within the effective pressure oscillations in cuff 14 . Pressure oscillations within the wearable cuff 14 have predetermined minimum (Amin) and maximum (Amax) values. The amplitude of vibration is calculated as the maximum value (Amax) minus the minimum value (Amm). If the maximum (Amax) and minimum (Amin) are shifted by the same amount, the resulting amplitude is unaffected. If only one of the maximum value (Amax) and minimum value (Amin) is changed, the vibration amplitude will be distorted.

For example, consider a pressure oscillation in the wearable cuff 14 that is maximum at a first time t=0 seconds and minimum at a second time t=0.5 seconds thereafter. The change in target inflation rate starts at t>0 and introduces pressure artifacts (or transients) over time. The maximum pressure oscillation (at t=0 seconds) is not affected. However, the pressure oscillation minimum (at t=0.5 s) will be affected. The magnitude of the effect depends on how much the pressure changes during the 0.5 seconds between the minimum and maximum pressure oscillations.

となる。 The pressure (or artifact) induced in the pressure signal due to changes in the target inflation rate of the wearable cuff 14 is a function of the system response HTotal(s) and the change in target inflation rate itself. In the worst case, the target inflation speed change (“ΔlnflationSpeed”) is the target inflation speed step (“Xstep”). It is equal to the target inflation speed after the change in inflation speed (herein referred to as the second inflation speed) minus the target inflation speed before the change in inflation speed (herein referred to as the first inflation speed). . The induced pressure due to the change in the first inflation rate of the wearable cuff 14 can be written as the convolution of the system response HTotal and the inflation rate step XsteP,

becomes.

となる。 The maximum value of this induced pressure is therefore the change in the first inflation rate multiplied by a scaling factor M1 (related to the system response Htotal),

becomes.

の最大変化に短い時間枠の持続時間を乗じた量を有することができる。 The induced pressure waveform due to the change in the first inflation rate of the wearable cuff 14 can (depending on the system) have a relatively long duration (e.g., on the order of seconds), resulting in multiple pressure oscillations in the pressure signal. can straddle. Here, a single pressure oscillation can exist during only part of the induced pressure waveform. In the short timeframe of a single pressure oscillation, the induced pressure is

, multiplied by the duration of the short timeframe.

となる。ここで、

は再び、第１の膨張速度の変化にシステム依存係数（Ｍ２と表記される）を乗じたものであり、

となる。 In order not to affect the pressure oscillation envelope, the maximum induced pressure must be much smaller than the change in the oscillation signal or negligible,

becomes. here,

is again the change in the first expansion rate multiplied by a system dependent factor (denoted M2),

becomes.

となる。 Between the minimum value (Amin) and the maximum value (Amax) of the actual pressure oscillation in the wearable cuff 14, the pressure changes from the minimum value (Amin) to the maximum value (Amax),

becomes.

となる。 Substituting equations (4) and (5) into equation (3) yields

becomes.

となる。 The duration between the minimum (Amin) and maximum (Amax) pressure oscillations at the wearable cuff 14 is a fraction (c) of the pulse rate (PR) as follows:

becomes.

となる。 The fraction c in equation (7) is not 50% due to the asymmetry of the pressure pulse between rising and falling edges. Substituting equation (7) into equation (6), we get

becomes.

The condition that the change in the induced pressure in the vibration signal is small is shown in Equation (11). With the desired change in the first inflation rate known and the pulse rate and amplitude measurable, the only potential unknowns in equation (11) are M2 and K1. M2 is a system-related parameter (Htotal) that is fixed and can be determined in advance (eg, during system design). The parameter K1 depends on c (which is the worst case pressure oscillation) and k (<1), which means that the induced pressure in the vibration signal is less than the effective pressure oscillation in the wearable cuff 14. It describes the extent to which it must be This parameter can be determined experimentally. Thus, at the instant of change in the first expansion rate, all parameters are known and it is predictable whether a desired change in the first expansion rate will result in an induced pressure in the vibration signal affecting the vibration amplitude. can be

As shown in equation (11), the degree to which the induced pressure in the vibration signal must be less than the effective pressure oscillations in the wearable cuff 14 depends on the amplitude of the pressure oscillations in the wearable cuff 14 and the subject's 18 pulse rate. depends on the number and This is logical. This is because small pressure vibration amplitudes are more susceptible to the induced pressure than large pressure vibration amplitudes. The same is true for pulse rate dependence. The greater the number of pressure oscillations in the induced pressure period, the smaller the impact on the amplitude of each pressure oscillation. Similarly, the smaller the number of pressure oscillations in a period of the induced pressure, the greater the impact on the amplitude of each of those pressure oscillations.

、及び従ってＭ２・ΔｌｎｆｌａｔｉｏｎＳｐｅｅｄが、システムＨｔｏｔａｌに依存する値により上限が設定され、

となる。 From equation (11), it can be seen that when (M2·ΔlnflationSpeed) is smaller than K1·(Amax−Amin)·PR, the induced vibration is considered to be small. The left-hand side of Eq. (11) is changed such that the induced pressure oscillations can be considered small by ensuring that the first expansion rate changes slowly, rather than having sharp steps in the expansion rate. be able to. This is accomplished by varying the first inflation rate during inflation of the wearable cuff 14 at a rate limited to a maximum value, as described above (at block 304 of FIG. 3). Thus, the rate at which the first inflation rate is changed during inflation of the wearable cuff 14 is limited. This saturates the derivative of the target pressure rate signal. By thus limiting the rate of change of the first expansion velocity, the maximum change in the oscillating pressure

, and thus M2·ΔlnflationSpeed is capped by a value that depends on the system Htotal,

becomes.

として更に単純化され、ここで、Ｍ３はシステム依存係数である。式（１１）に式（１３）を代入することにより、

となる。 Here, the maximum value (or rate limit) of the rate at which the first expansion rate is changed is denoted by "RL". ΔlnflationSpeed is not part of this equation. This is because the maximum rate (RL) at which the first expansion rate is changed limits the rate at which the step is performed. f(RL, Htotal) is

where M3 is a system dependent coefficient. By substituting equation (13) into equation (11),

becomes.

となる。 From equation (15), it can be seen that choosing an appropriate fixed value for the maximum rate of change (RL) of the first expansion velocity results in small induced artifacts compared to pressure oscillations. That is, based on the worst case vibration amplitude (Amax-Amin) and the worst case pulse rate (PR), the maximum rate (RL) at which the first inflation rate is changed can be selected. . Alternatively, the maximum rate at which the first inflation rate is changed (RL) is the vibration amplitude (Amax-Amm) and vibration frequency (i.e., pulse rate) of a signal indicative of pressure vibrations detected within wearable cuff 14. can be a value proportional to both the number (PR)) and

becomes.

In equation (16), the factor K2 depends on the system transfer and may be chosen such that K2<=K1/M3. When selecting coefficient K2, limiter 31 requires amplitude and pulse rate as inputs. These values can be determined from signals indicative of pressure oscillations detected within wearable cuff 14 during inflation of wearable cuff 14 using standard signal processing techniques. In some embodiments, factor K2 may be adaptive. For example, factor K2 may depend on system parameters (eg, resistance of at least one supply tube 16 and/or compliance of wearable cuff 14).

Alternatively or additionally that the maximum rate at which the first expansion rate is changed (RL) depends on the vibration amplitude and/or vibration frequency (as in equation (16)), the first The maximum rate at which the inflation rate is changed (RL) may also incorporate a dependence on the magnitude of the first inflation rate change (or inflation rate step size, "ΔlnflationSpeed").

Thus, in some embodiments, the maximum rate (RL) at which the first inflation rate is changed may be adaptive. For example, in some embodiments, the maximum rate at which the first inflation rate is changed (RL) may be a value that depends on at least one parameter. As previously mentioned, examples of at least one parameter include, but are not limited to, pulse rate obtained from subject 18 (or wearable cuff 14 ) during inflation of wearable cuff 14 at the first inflation rate. frequency of a signal indicative of pressure oscillations detected within), amplitude of a signal indicative of pressure oscillations detected within wearable cuff 14 during inflation of wearable cuff 14 at the first inflation rate (or oscillation amplitude of the beat) , the difference (or speed step size) between the first inflation rate and the second inflation rate, and any one or more of one or more characteristics of the system 10 including the wearable cuff 14 . In some embodiments, the one or more characteristics of system 10 can include any one or more of the size of wearable cuff 14 and the resistance detected by system 10 .

In other embodiments, the maximum rate at which the first inflation rate is changed (RL) may be a fixed value (or fixed rate).

In some embodiments, the first inflation rate may be changed at a constant rate. Alternatively, in other embodiments, the first inflation rate may be changed at a variable rate. In some embodiments, device 12 may be configured to change the first inflation rate based on the pulse rate obtained from subject 18 during inflation of wearable cuff 14 at the first inflation rate. A pulse rate is obtained from the subject 18, for example, by analyzing a pressure signal indicative of the pressure within the wearable cuff 14 during inflation of the wearable cuff 14 at the first rate of inflation to determine the subject's 18 pulse rate. may be For example, pulse rate may be determined as the frequency of the pressure signal indicative of the pressure sensed within wearable cuff 14 . Varying the first inflation rate by a value proportional to the vibration amplitude and pulse rate of the subject 18 allows the duration of any blood pressure measurement to be as short as possible without introducing artifacts.

In some embodiments, the first inflation rate may be changed at a rate that is the maximum rate (RL) at which the first inflation rate is changed. Alternatively, in other embodiments, the first inflation rate may be changed at a rate that is less than the maximum rate (RL) at which the first inflation rate is changed. In some embodiments, the maximum rate at which the first inflation rate is changed (RL) may range from 1-16 mmHg/s ² .

FIG. 4 is a schematic illustration of an exemplary signal showing artifacts due to changes in the inflation rate of wearable cuff 14 during blood pressure measurement according to existing techniques. 5-9 are schematic illustrations of exemplary signals exhibiting reduced artifacts according to some embodiments implementing apparatus 12 described herein. Reference is now made to FIGS. 4-9 to illustrate the minimization of artifacts due to changes in the rate of inflation of the wearable cuff 14 that can be achieved using the device 12 described herein.

FIG. 4(a) is a schematic illustration of the time course of the expansion rate "Infl.S" according to the existing method. As shown in FIG. 4(a), at t=3.5 s, the inflation rate changes from the first inflation rate of 6 mmHg/s to the second inflation rate of 15 mmHg/s. 4(b) is a schematic illustration of an undisturbed (or undistorted) pressure signal “Osc.” showing pressure oscillations within the wearable cuff 14 over time during inflation of the wearable cuff 14. FIG. be. FIG. 4(c) is a schematic illustration of the "Art." artifact introduced into the pressure signal over time by changes in the rate of inflation. This artifact is the response of the system 10 including the wearable cuff 14 excited by a velocity step size (here 9 mmHg/s).

FIG. 4(d) is a schematic illustration of a disturbed (or corrupted) pressure signal when the pressure signal is disturbed (or corrupted) by an artifact. Thus, FIG. 4(d) illustrates the combination of the artifact and the pressure signal, indicating that the pressure oscillations within the wearable cuff 14 are disturbed by the artifact. This artifact disturbance results in a perturbation of the upper and lower envelopes, as indicated by the dashed lines. FIG. 4(e) is a schematic representation of the resulting envelope "Env." of the (original or true) uncorrupted pressure signal "Tr." and the corrupted (or corrupted) pressure signal "Corr." It is an explanatory diagram. From the discussion of FIGS. 5-9 that follow, it will be seen that the use of the device 12 described herein results in artifacts due to changes in the inflation rate of the wearable cuff 14 compared to existing techniques such as illustrated in FIG. It will be seen that it can be minimized in comparison.

5 and 6 illustrate that in the exemplary embodiment shown in FIG. 5 the first inflation rate is changed at a rate limited to a maximum of 16 mmHg/s ² and the exemplary embodiment shown in FIG. 4 except that in a preferred embodiment the first inflation rate is changed at a rate limited to a maximum of 8 mmHg/ ^s2 . As can be seen from FIG. 5 compared to FIG. 4, when the rate at which the first expansion velocity is changed is limited to a maximum value of 16 mmHg/ ^s2 , compared to no rate limitation as in FIG. As a result, the error in the disturbed (or corrupted) pressure signal is much smaller. Similarly, as can be seen from FIG. 6 compared to FIG. 4, when the rate at which the first inflation velocity is changed is limited to a maximum value of 8 mmHg/ ^s2 , the perturbed (or corrupted) pressure signal The error is less than with a rate limit of 16 mmHg/s ² as in FIG. 5 and much less than without rate limit as in FIG. 4, and is in fact virtually eliminated.

Figures 7-9 also show that in the exemplary embodiment shown in Figures 7-9, the first inflation rate is changed at a rate limited to a maximum of 8mmHg/ ^s2 . , as in FIG. 7-9 illustrate the effects of this rate limiting at three different vibration settings: 70 beats per minute with a peak-to-peak vibration amplitude of 1 mmHg in FIG. 7 and every 70 beats per minute in FIG. 70 beats per minute, FIG. 9 shows the effect of 210 beats per minute with a peak-to-peak vibration amplitude of 1 mmHg.

As can be seen from FIGS. 7-9 when compared with FIG. 4, when the rate at which the first inflation velocity is changed is limited to a maximum value of 8 mmHg/ ^s2 , for each of the different vibration settings, as in FIG. There is much less error in the corrupted (or corrupted) pressure signal compared to when rate limiting is not used. As can also be seen from Figures 7-9, the artifact is the same for each of the different vibration settings. However, the effect on the resulting pressure envelope is different for each different vibration setting based on the amplitude and frequency of vibration of the pressure signal. If the vibration is small and/or slow compared to the artifact, the artifact can still disturb the signal (as illustrated in FIG. 7). If the artifact is small compared to the oscillation (as shown in Figure 8) or if the oscillation is fast relative to the artifact (as shown in Figure 9) the resulting pressure envelope will be less affected. For fast oscillations (as shown in FIG. 9), the oscillations exhibit dips due to artifacts, but the resulting pressure envelope is minimally affected by the artifacts. This is because artifacts affect both the minimum and maximum values of each oscillation.

Thus, as can be seen from FIGS. 5-9, the device 12 described herein for limiting the rate at which the first inflation rate of the wearable cuff 14 changes compared to existing technology such as that illustrated in FIG. to reduce or eliminate artifacts (or transient effects) that would otherwise be induced by changes in the first inflation rate from the signal indicative of pressure oscillations within the wearable cuff 14 during inflation. know that it can be done.

In any of the embodiments described herein, device 12 may be further configured to acquire signals indicative of pressure oscillations detected within wearable cuff 14 during inflation of wearable cuff 14 . In these embodiments, device 12 (eg, controller 32 of device 12) may be further configured to determine (or measure) the blood pressure value of subject 18 based on the acquired signal. Alternatively, a module external to device 12 (e.g., separate from device 12 or separate from device 12) outputs a signal indicative of pressure oscillations detected within wearable cuff 14 during inflation of wearable cuff 14. and determine (or measure) the blood pressure value of the subject 18 based on the acquired signal. Thus, device 12 (or an external module) may be configured to determine the blood pressure value of subject 18 during inflation of wearable cuff 14, according to some embodiments.

Device 12 is for use in inflation-based blood pressure measurements, as the blood pressure value of subject 18 is determined based on signals acquired during inflation (or an inflation phase) of wearable cuff 14 . More specifically, device 12 is for use in inflation-based non-invasive blood pressure (iNIBP) measurement. In some embodiments, the acquired signal may be in a frequency range corresponding to a heart rate range of 30 beats/minute to 300 beats/minute. For example, according to some embodiments, the acquired signal may be in the frequency range of 0.5 Hz to 5 Hz.

In any of the embodiments described herein, at least one or all of the steps that device 12 is configured to perform can be automated.

A computer program product including a computer-readable medium is also provided. A computer readable medium has computer readable code embodied therein. The computer readable code, when executed by a suitable computer or processor, configures the computer or processor to perform the methods described herein. A computer-readable medium can be, for example, any entity or device capable of carrying a computer program. For example, a computer readable medium may include a data storage medium such as a ROM (CD-ROM or semiconductor ROM), or a magnetic recording medium (eg a hard disk). Additionally, a computer-readable medium may be a transmissible carrier such as an electrical or optical signal, which may be transmitted via electrical or optical cables, or by radio or other means. When the computer program product is embodied in such signals, the computer readable medium may be constituted by such cables or other devices or means. Alternatively, the computer readable medium may be an integrated circuit having a computer program embedded therein, the integrated circuit being configured to carry out the methods described herein, or performing the methods described herein. used to run.

Thus, apparatus, methods, and computer programs are provided herein that address limitations associated with existing technology.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art who practice the principles and techniques described herein, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. The computer program may be stored or distributed on any suitable medium, such as optical storage media or solid-state media, supplied with or as part of other hardware, but may also be distributed over the Internet or other wired network. Or it may be distributed in other forms, such as via a wireless communication system. Any reference signs in the claims should not be construed as limiting the scope.

Claims (12)

A device for controlling a wearable cuff used for blood pressure measurement,
the wearable cuff is inflatable to pressurize a target measurement site;
the device is configured to initiate inflation of the wearable cuff at a first inflation rate and to vary the first inflation rate during inflation of the wearable cuff;
the first inflation rate is changed at a rate limited to a maximum value;
The maximum value is
a pulse rate obtained from the subject while inflating the wearable cuff at the first inflation rate; and/or
an amplitude of a signal indicative of pressure oscillations detected within the wearable cuff while inflating the wearable cuff at the first inflation rate;
The device that relies on . 2. The device of claim 1, wherein the device changes the first inflation rate to a second inflation rate during inflation of the wearable cuff. said device comprising:
2. Varying the first inflation rate by increasing the first inflation rate during inflation of the wearable cuff; or decreasing the first inflation rate during inflation of the wearable cuff. Or the device according to 2. 4. Apparatus according to any one of the preceding claims, wherein the first inflation rate is changed at a rate that is at or below a maximum value. 5. Apparatus according to any one of the preceding claims, wherein the first inflation rate is changed at a rate that is variable or at a constant rate. 6. A device according to any one of the preceding claims, wherein said maximum value is 16 mmHg/s2 or less. 7. The device of any one of claims 1-6, wherein the device changes the first inflation rate based on the pulse rate obtained from the subject while inflating the wearable cuff at the first inflation rate. 3. Apparatus according to paragraph. said device comprising:
obtaining a signal indicative of pressure oscillations detected within the wearable cuff during inflation of the wearable cuff;
8. The apparatus of any one of claims 1-7 , further configured to determine a blood pressure value of the subject based on the acquired signal. 9. The apparatus of claim 8 , wherein the acquired signal is in the frequency range of 0.5Hz to 5Hz. A system for use in blood pressure measurement, comprising:
a device according to any one of claims 1 to 9 ;
and a wearable cuff that is inflatable to pressurize a measurement site of interest. A method for controlling a wearable cuff used for blood pressure measurement comprising:
the wearable cuff is inflatable to pressurize a target measurement site;
The method includes:
initiating inflation of the wearable cuff at a first inflation rate;
changing a first inflation rate during inflation of the wearable cuff;
the first inflation rate is changed at a rate limited to a maximum value;
The maximum value is
a pulse rate obtained from the subject while inflating the wearable cuff at the first inflation rate; and/or
an amplitude of a signal indicative of pressure oscillations detected within the wearable cuff while inflating the wearable cuff at the first inflation rate;
depends on
Method. 12. A computer program product comprising computer readable code which, when executed by a suitable computer or processor, is configured to cause said computer or processor to perform the method of claim 11 .

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